Don't. If you want custom cables try cablemod.com or buy over cable sleeves.
https://www.gamersnexus.net/guides/2702-psa-on-mixing-modular-psu-cables-dont-do-it
Because theyre cheaper...He's not planning on mixing cable brands. He's planning on using extensions.
Which is still a bad idea.
Why pay for extensions when aftermarket individually-sleeved-cables from Cablemod, Ensourced, Corsair, etc. that are made SPECIFICALLY for your PSU?